The present invention relates to a fluidized bed reactor comprising a reactor chamber provided with substantially vertical side walls laterally confining a bed of fluidizable particulate material and a gas distributor plate, through which primary gas is fed into the reactor chamber. The reactor chamber has an inlet for particulate bed material and an outlet in its upper part for exhausting gases.
The particulate bed material in the fluidized bed reactor may in part be formed by the material which is to be treated within the reactor. Alternatively, it may be inert, or take part in the treatment, or take part in the heating of the bed. The particulate material is fluidized with primary gas supplied through gas distribution means mounted on the gas distributor plate. The gas distributor plate also provides a support for the particulate bed material.
The fluidizing medium--like the bed material --used may be inert or take part in the treatment to be effected, or take part in the heating of the bed.
Fluidized bed reactors are presently used for many different purposes such as, for example, combustion, gasification, and chemical and metallurgical processes, because they are capable of producing: an efficient contact between a gas and a solid, liquid, or gaseous material to be treated; a high reaction rate; and even temperature and good controllability of the process. The larger the reactor, however, the more difficult it is to carry out stable operations and to control the reactor during changing process conditions. In large reactors it is especially difficult to achieve even distribution of fluid and/or particulate material throughout the whole cross sectional area of the reactor chamber. Uneven distribution may cause significant problems.
In combustion processes, all of particulate, liquid, or gaseous fuels, or a mixture of these, may be combusted in the fluidized bed reactor. The fuel --as well as additives needed for gas cleaning purposes or other chemical reactions--is usually introduced through nozzles in the side walls or through nozzles in the gas distributor plate.
Fluid fuel such as oil is usually introduced through oil lances arranged in openings in the side walls approximately at a level 0.5 m above the gas distributor plate. The oil is injected with pressurized air as distribution medium but can normally reach only about 1 m into the reactor chamber. In big reactors where the distance between the side walls and the center of the reactor chamber exceeds the distance of the oil penetration into the bed, the distribution of oil will be unsatisfactory.
The above mentioned problem cannot be overcome by increasing the oil supply through the lances as the oil supply has to be limited to about 500 kg/h, i.e. the energy density should in general be less than 7500 kJ/m.sup.2, in order to prevent overheating and agglomeration of bed particles at locations close to the oil supply. Similar problems will occur when distributing other fluid fuels or reactants into large fluidized bed reactors.
At present there are known fluid fuel nozzle arrangements, such as described in U.S. Pat. No. 4,165,040, which comprise in combination a fluid fuel nozzle and a fluidizing gas nozzle, the combinations being evenly distributed on a distributor plate. The fluid fuel injection nozzles have inlet means for fluidizing gas in a sleeve surrounding the fuel nozzle. This arrangement allows an atomization of fluid fuel. For example, an even distribution of oil with primary air into a combustor may be provided.
A severe problem remains however. The nozzles operate at a high temperature and in a high stress environment, which may cause clogging of the fuel nozzles. It is therefore necessary to periodically check the fuel nozzles and replace deteriorated nozzles in order to ensure an even combustion in the reactor. The risk of clogging is especially high at load variations when the pressure drop over the nozzles changes. Cleaning of nozzles in a grid plate is very complicated during running conditions. Either the whole system has to be shut down for cleaning, or very complicated replaceable nozzle arrangements must be utilized.
U.S. Pat. No. 4,259,088 discloses a fluid fuel distribution arrangement in a fluidized bed apparatus according to which fluid fuel is introduced though horizontal conduits embedded in non-fluidized particulate bed material. The straight fluid conduits are easy to clean even during running. The conduits terminate into depressions in the non-fluidized bed material, the particulate bed material being fluidized in the depressions. This arrangement requires gas distribution nozzles of at least two different heights in the distributor plate for forming a contoured interface between the non-fluidized and the fluidized particulate bed material. The nozzles reaching above the non-fluidized layer of particulate material have to be much higher than the nozzles in the wells. Further the different gas distribution nozzles have to have differently dimensioned openings in order to get an even supply of air over the whole cross-sectional area higher up in the reactor chamber. This is a complicated construction.
The depressions or wells are relatively small and preferably 5-6 inches deep. The introduction of both oil and fluidizing air into such limited zones causes a great risk of agglomeration. It is hard to get an even distribution of nozzles in the relatively narrow area. Uneven distribution of nozzles gives uneven fluidization of particles. Further the oil can wet the bed particles in the wells and cause them to stick to each other forming larger non-fluidizable particles. There is also a risk of the temperature rising too high when fuel and air nozzles are too closely arranged. The fluid fuel nozzles can hardly be arranged at a higher level above the air nozzles when using this arrangement with non-fluidized particulate material covering the fluid conduits. Very large amounts of non-fluidized bed material would be needed to protect the conduit at a high level above the grid and large amounts of bed material would need a very strong support plate. A thick layer of non-fluidized particulates would further lead to very deep, inadequate depressions in the non-fluidized layer.
A fluidized bed reactor is disclosed in FI patent 59860 wherein the reactor chamber is divided by a partition wall, made of water tubes, into two separate fluidized bed sections. The particulate fuel is supplied into the separate sections through a pipe disposed within the central partition wall between the bed sections. The fuel supply system is not easy to clean and does not provide an even distribution of fuel throughout the cross sectional area of the reactor chamber.
It is an object of the present invention to provide even feed and distribution of fluid in large fluidized bed reactors over the whole cross sectional area of the reactor. The fluid may be supplied into the reactor at different distances from the side walls of the reactor. Also according to the present invention, an even distribution of fluid fuel or reactant into large scale fluidized bed reactors is provided through reliable and easy-to-clean fluid inlet means. According to the invention the risk of agglomeration of particulate material in the bed due to fluid distribution is minimized.
According to one aspect of the present invention, there is provided a fluidized bed reactor into which primary gas is distributed, preferably through distribution nozzles in the bottom plate i.e. gas distributor plate, the nozzles having gas outlet openings at the bottom plate or at a level a short distance above the surface of the bottom plate. The primary gas is preferably introduced into the reactor chamber at a substantially constant distance from the bottom plate over the entire cross-sectional area of the reactor chamber. It is possible to arrange several different distributor conduits in the partition if needed.
Fluid supplying means are disposed in the reactor chamber at a distance above the primary gas distribution level. The fluid supplying means comprise a fluid conduit connected to a fluid inlet opening in one side wall. The fluid conduit extends preferably horizontally into the interior of the reactor chamber for distribution of fluid into interior locations too far from the side walls to be reached by fluid injected at the periphery (i.e. wall) of the reactor chamber. The fluid outlet end of the fluid conduit may be at a distance greater than about 1000 mm from the side wall, and between about 100-1000 mm above the primary gas distribution plate (e.g. preferably at a distance between about 300-600 mm above the primary gas introduction level).
The fluid conduit is disposed inside an upright partition mounted on the bottom plate. The partition protects the fluid conduit from erosive and deteriorating conditions in the reactor chamber. The partition covering the fluid conduit extends preferably from the side wall substantially for the whole length of the fluid conduit into the interior of the reactor chamber. The partition may divide the lower part of the fluidized bed partly in sections. Fluid outlets may also be arranged directly on the side walls to distribute fluid in the vicinity of the walls.
The aforesaid upright partition--which preferably is about 100-400 mm wide, to allow the fluid conduit to pass therethrough--is preferably greater than about 1000 mm long, depending on the distance between opposite walls in the reactor chamber. There can be a plurality of fluid conduit upright partition systems reaching various distances into the reactor chamber to ensure that the fluid is evenly distributed over the whole cross sectional area of the reactor chamber. The upright partition may, for example, have a height between about 200-1100 mm above the bottom plate. The partition is preferably made of a refractory or other suitable material resistant to the eroding hot conditions in the reactor chamber. The partition is generally thick enough to hold the fluid conduit and to insulate the conduit to a certain extent from the heat in the reactor chamber.
The present invention provides a simple construction for introduction of fluid into a fluidized bed reactor. The invention may be utilized, e.g., in fluidized bed combustors using liquid fuel--such as oil--or fine particulate fuel suspensions--such as coal suspended in water or steam. An oil-lance may be disposed in an upright partition at a level at which the oil and the primary gas do not negatively interfere with each other. The present invention can also be used to introduce suspensions containing additives, e.g. for gas cleaning purposes, into a combustor. Various kinds of pumpable fluids may be evenly distributed into fluidized bed reactors utilizing the present invention.
According to the present invention, it is possible to achieve the following advantages:
more efficient distribution of fluids and thus better mixing of fluid into large scale fluidized reactors; PA1 minimized risk of local overheating and agglomeration of particles; PA1 ease of cleaning fluid supply means; and PA1 no need for different types of gas distributor nozzles at different locations in the reactor.